French patent 1,593,557 discloses an apparatus for internal irradiation, comprising a distributor for composing a ball row out of radio-active and neutral balls, at lease one applicator tube adapted to be introduced into a body cavity to be irradiated, and a pneumatic transport system by which a ball row may be inserted in an applicator tube and removed from the same.
In an apparatus of this kind, the applicator tube may form a part of a Fletcher applicator comprising three applicator tubes adapted to be introduced into a body cavity, and each adapted to receive a radio-active material.
In order that the irradiation may be exactly applied to the required locations, the radio-active material is introduced in the shape of a ball row consisting of contiguous radio-active and neutral balls. Thus, an irradiation occurs at the location of the radio-active balls, and there is no irradiation at the locations of the neutral balls. The ball row is composed beforehand, and is pneumatically transferred to the desired applicator tube. Usually, each ball row contains a fixed number of balls, for instance 48 balls.
The pneumatic pressure moves the ball row so far into the internal channel in the applicator tube that the foremost ball abuts against the end wall of this channel. After termination of the irradiation, the ball row is removed from the applicator tube by a pneumatic pressure in the opposite direction. For this purpose, the applicator tube may be double-walled, so that it consists of an inner casing forming the internal channel receiving the ball row, and an outer casing surrounding the same. The air for removing the ball row from the applicator tube is supplied to the outer casing, which communicates with the internal channel through an opening at the end of the inner casing.
In order that the irradiation is applied to the correct locations, it is, of course, necessary that the balls stay in place during the irradiation. For this purpose, it is usual to maintain the pneumatic pressure used for introducing the balls during the irradiation, so that the ball row is pressed against the end wall of the inner casing of the applicator tube.
It has been found, however, that the balls do not always stay in place in practice, since the air exerting the pneumatic pressure may leak past the balls of the ball row, in particular due to the pressure of the opening in the end wall of the inner casing. This leakage also leads to an excessive air consumption, which may involve a deposition of dirt on the tube walls. In this connection, it is pointed out that the total duration of the irradiation may amount, for certain patients, to more than 40 hours.